Periodontitis is a chronic inflammatory disease of the periodontium characterized by bursts of disease activity and longer periods of remission. Ligature-induced periodontitis provides a model with a similar microflora in which the rate of disease can be accelerated. Induction of a heightened immune response via immunization prior to the usual establishment of a periodontopathic organism (such as B. gingivalis) may delay or reduce its colonization and thereby influence the development and/or severity of periodontitis. If immunization could provide some degree of protection, it would provide a better understanding of the pathogenesis of periodontitis and would potentially be of value in treatment. The purpose of this investigation is to study the influence of immunization with a predominant cultivable microorganism on host bacterial interactions during the progression to periodontitis in a monkey model. The specific aims are to: 1. Isolate the predominant cultivable subgingival microflora, determine the serum and gingival crevicular fluid antibody levels to these organisms in cynomolgus monkeys by ELISA during the progression from gingivitis to ligature-induced, advanced periodontitis and describe relationships observed. 2. Examine the efficacy of monkey immunization with Bacteroides gingivalis isolated from monkeys by monitoring the clinical, histological, bacterial and humoral responses during ligature-induced periodontitis. It will be determined if the colonization by B. gingivalis, the rate of disease progression and/or the extent is of disease is modified from a group of sham-immunized, ligated monkeys and a group of B. gingivalis immunized non-ligated monkeys.